LanguageDomains.php

<?php

namespace Drupal\language\Plugin\migrate\process;

use Drupal\migrate\MigrateExecutableInterface;
use Drupal\migrate\Plugin\migrate\process\ArrayBuild;
use Drupal\migrate\Row;

/**
 * This plugin makes sure that no domain is empty if domain negotiation is used.
 *
 * @MigrateProcessPlugin(
 *   id = "language_domains",
 *   handle_multiples = TRUE
 * )
 */
class LanguageDomains extends ArrayBuild {
    
    /**
     * {@inheritdoc}
     */
    public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
        if ($row->getSourceProperty('domain_negotiation_used')) {
            global $base_url;
            foreach ($value as $old_key => $old_value) {
                if (empty($old_value['domain'])) {
                    // The default language domain might be empty.
                    // If it is, use the current domain.
                    $value[$old_key]['domain'] = parse_url($base_url, PHP_URL_HOST);
                }
                else {
                    // Ensure we have a protocol when checking for the hostname.
                    $domain = 'http://' . str_replace([
                        'http://',
                        'https://',
                    ], '', $old_value['domain']);
                    // Only keep the host part of the domain.
                    $value[$old_key]['domain'] = parse_url($domain, PHP_URL_HOST);
                }
            }
        }
        return parent::transform($value, $migrate_executable, $row, $destination_property);
    }

}